LG 75SM9400PTA Service Manual page 36

Standard Repair Process
symptom
First of all, Check whether all of cables between board is inserted properly or not.
(Main B/D↔ Power B/D, Each Cable for Panel, Speaker Cable, IR B/D Cable,,,)
No video
Normal
Normal audio
audio
N
Move to No
video/No audio
※Precaution ☞A4 & A2
Always check & record S/W Version and White
Balance value before replacing the Main Board
A. Video error
Error
No video/ Normal audio
☞A1
Y
Check Back Light
On with naked eye
☞A9
Check Power Board VLED output
☞A9
Y
Check Power Board
On
13.2V etc.
N
☞A10
Y
Normal Error Check LED Driver BD by
LED indicator
voltage
N
Repair Power
End
Board or parts
Replace Main Board
1
Established
date
Revised date
Y
Normal Replace T-con/Main
voltage Board or module
N
Repair Power
Board or parts
LED
Y
Driver BD
error
N
Replace Module
Re-enter White Balance value
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1/16
Replace LED
Driver BD
End